Photocatalyst materials are particularly excellent in their substance decomposition ability and ultra-hydrophilicity function. Utilizing such function, photocatalyst materials are used for air purification, water purification, decomposition of organic substances, and anti-fogging and anti-soiling coating material.
Methods and apparatuses for producing such photocatalyst materials are classified into two types: dry deposition methods and wet deposition methods.
As dry deposition methods, there are PVD (physical vapor deposition) and CVD (chemical vapor deposition). As photocatalyst producing methods based on PVD, there have been Patent References 1 and 2. As photocatalyst producing methods based on CVD, there have been Patent References 3 and 4 and the like.
As wet deposition methods, there have been sol-gel methods (Patent References 4 and 6) and coating methods (patent References 5 and 6).
In the PVD method of Patent Reference 1, when the oxygen concentration is set at 10 to 50% in a reaction space in a depressurized state of 0.4 to 3 Pa, which is close to vacuum, Ti,Si metal is installed as a target. Depressurized plasma is formed by 30-kW high-frequency magnetrons in the reaction space, and particles sputtered from the target are oxidized by the plasma, thus forming a photocatalyst film on a substrate.
In the PVD method of Patent Reference 2, ozone gas emitted from a double-tube ozonizer is used. When oxygen and ozone pressure division is performed to 0.01 to 2 Pa in a reaction space in a depressurized state of 3 Pa or less, which is close to vacuum, Ti,Si metal is installed as a target. By a sputtering device that is caused to discharge DC magnetrons, depressurized plasma is formed in the reaction space and particles sputtered from the target are oxidized by the plasma, thus forming a photocatalyst film on a substrate.
Patent References 3 and 4 disclose photocatalyst film forming methods based on thermal CVD methods. In these methods, deposition component gas (for example, Ti (OiPr)) and nitrogen (2% NH3) are preheated at 180° C. and supplied into a CVD device, and react with oxygen gas of approximately 0.012 MPa supplied in the CVD device, thus forming a photocatalyst material film (in this case, TiO2) on the surface of a processing subject heated to several hundred degrees.
In the sol-gel methods of Patent References 4 and 6, a glass is coated with Ti(OEt)4-EtOH-36% HCL solution and dried at several hundred degrees for several minutes to form a film, which is baked at a predetermined temperature to form a photocatalyst material of TiO2. As the coating materials, TiO2 sol and various crystalline precursors are subjects of patent.
The coating methods of Patent References 5 and 6 are methods of coating a substrate with liquid containing a TiO2 material to from a film and then heating and gradually cooling to lower the temperature, thus forming a photocatalyst material.
Meanwhile, there are Patent References 7 to 11 as prior arts utilizing photocatalyst and discharge.
In Patent Reference 7, inert gas and oxidative gas are supplied into a vacuum container, and crystalline titanium oxide is produced by a sputtering method based on continuous discharge plasma such as glow discharge at a low pressure.
Patent Reference 8 discloses a producing method in which a target source such as titanium oxide to be a photocatalyst film material is provided in vacuum and sputtering is performed using high-frequency discharge equivalent to continuous discharge plasma in a low-pressure dilute gas.
Patent Reference 9 discloses a method of manufacturing an amorphous photocatalyst film by sputtering a sintered conductive target such as titanium oxide and niobium oxide, tantalum oxide and the like in an atmosphere that can be depressurized.
In Patent Reference 10, the surface of a substrate is coated with titanium-containing oxide or the like and nitrided by AC glow discharge, which is continuous discharge plasma, in a mixed gas containing ammonium gas and nitrogen gas at an atmospheric pressure, thus modifying the photocatalyst film.
Patent Reference 11 discloses a device that produces ozone by increasing dissociation of oxygen compound gas and oxygen compound or acceleration of dissociation of oxygen gas by oxygen compound gas or oxygen compound and discharge light, and suggests that if metals are laminated and dielectric barrier discharge (silent discharge) is caused to generate ozone, a metal oxide film (photocatalyst material) is formed.
Patent Reference 1: JP-A-2002-348665
Patent Reference 2: JP-A-2001-073116
Patent Reference 3: JP-A-10-202776
Patent Reference 4: JP-T-11-512337
Patent Reference 5: JP-A-2003-1129490
Patent Reference 6: Japanese Patent No. 2,756,474
Patent Reference 7: JP-A-2004-137101
Patent Reference 8: JP-A-2001-104798
Patent Reference 9: JP-A-2001-25666
Patent Reference 10: JP-A-2003-321782
Patent Reference 11: JP-A-2004-359537